Ultrasound imaging systems have become a well accepted and important modality of diagnosis and guidance in many healthcare fields. For example, fetal monitoring, abdominal soft tissue study, and cardiac monitoring have all incorporated ultrasound systems as an essential aspect of effective diagnosis and treatment. Real time systems, where an organ or organism motion and development is observed as it occurs, has allowed practitioners to review many physiological conditions in vivo, in substitution for traumatic exploratory surgery or essential uncertainty as to the nature of the patient's condition.
In accordance with the knowledge of those of ordinary skill in the art, real time scanning systems work in a number of ways, including scanning an area of tissue by physical movement of an ultrasound transducer. In some systems, the transducer is coupled directly to the body of the patient, whereas in other systems the transducer is spatially separated from the body of a patient by a sonically conductive water path. In either case, as the transducer is "wobbled," typically by a stepping motor, the transducer is alternately conditioned to transmit a pulse of sonic energy into a tissue region, and then to receive echoes resulting from passage of the pulse through tissue interfaces. Electronic signal processing display apparatus assembles information resulting from the echoes, and based on the transducer position and local conditions, and upon the relative timing of the pulse transmission and echo receipts, a representation or image of the irradiated tissue is assembled.
The description of a preferred apparatus commonly used in ultrasound mammary scanning can be seen in co-pending Application No. 109,947 of Mezrich et al entitled Ultrasound Mammary Scanning Apparatus and filed Jan. 7, 1980. In accordance with the system described therein, the patient is conveniently positioned with the breast downwardly suspended in a tank of water, and from beneath, an ocillating or "nodding" transducer is scanned across the breast area, yielding a succession of spaced apart "B" scanned images. In the aggregate, these scans depict substantially all tissue within the breast, subject only to the limits of the resolution of the system with respect to each scan, and the spacing of the separate scans.
In order to accurately interpret the sonic image produced by such an apparatus, the diagnostician must be afforded information as to the size and accuracy of the informational bits composing the sonic image displayed. In short, he must be able to determine the resolution of the ultrasound transducer apparatus in order to accurately interpret the image produced. In addition, he must be able to test, on a convenient, systematic basis, the reliability and accuracy of the scanning apparatus.
The prior art solutions to these problems have heretofore involved the placement of straight wire phantoms within the acoustic energy field. Typically, these wires are held in some mounting device and arranged in pairs that are consecutively spaced apart with varying dimensions.
As the transducer head scans these consecutive pairs of wires, a transition point will be reached at which the transducer will first be capable of distinguishing or resolving the individual wires forming the pairs. The distance between the individual wires at the transition point is indicative of the resolution capability of the scanning apparatus.
This system of pairs of wires poses several problems to the technician attempting to utilize such a device to determine the accuracy and resolution of the scanning apparatus in question. Specifically, a wire presents a very small specular surface to the transducer beam and consequently, alignment of the wire becomes exceptionally critical in accordance with the well known laws of optics. Virtually only those acoustic waves impinging perpendicularly to the wire are reflected back to the transducer. All other impinging waves are reflected at varying angles and do not reach the transducer. Consequently, as the wire is tipped, great changes in image brightness result. Typically, however, as the image becomes brighter, it also becomes larger and therefore brightness must be continuously monitored in order to determine whether the increased size of the wire image is due to poor resolution or whether it is due to greater reflection of sound into the receiver. Further, such a system requires a great number of pairs of wires in order to afford the necessary range of spacings to adequately determine resolution.
It is an object of the present invention to reduce the number of wires required in order to effectively permit determination of resolution. It is a further objective that the critical degree of care required in the alignment of the straight wires with respect to the acoustical receiver be reduced so as to diminish the associated problems of dim, non-existent, or greatly changing images.